Write digit_product(n) that multiplies all the digits of the non-negative integer n together and returns the result. For n = 0 the answer is 0.
Examples
Input: n = 234
Output: 24
Explanation: 2 * 3 * 4 = 24
Input: n = 105
Output: 0
Constraints
0 <= n <= 10**18
Goals
- Accumulate with multiplication instead of addition
- Pick a sensible starting value for a product